Semiconductor lasers have been developed rapidly in recent years. There are however many potential applications of such lasers, such as satellite-borne operation, where reliability and power conversion efficiency limitations have generally prevented their use.
Relatively recent developments of semiconductor lasers have resulted in the increasing availability of high reliability devices, for example, with lifetimes as high as 10.sup.6 hours. Moreover, while certain populations of such devices have been determined to have a high infant mortality rate, the devices can be screened out so that the remaining devices in those populations are characterized by a substantial uniform long life, for example, (on the order of 100-1,000 years) life.
In addition, the recently developed semiconductor lasers, although relatively low power, have been becoming relatively inexpensive, highly power efficient, and controllable in terms of wavelength selectivity.
Generally, semiconductor lasers have reached the point where even large arrays of such lasers can be highly reliable and characterized by a relatively high efficiency power conversion, while maintaining a relatively low cost per laser. U.S. Pat. No. 4,246,548 and Phillip-Rutz, E.M., "Spatially Coherent Radiation From an Array of GaAs Lasers", Applied Physics Letters, Vol. 26, No. 8, April 1975, pp. 475-477, each disclose an external cavity laser including a monolithic array of laser diodes. As a result of the close proximity of the laser diodes in the monolithic array structure, the power dissipation density of these configurations is substantially limited. There are no prior art known approaches to overcome this power dissipation density limitation in coupling large numbers of relatively low power semiconductor laser devices to produce a relatively high power (for example, on the order of 1 kW), coherent optical beam.
It is an object of the present invention to provide an external cavity semiconductor laser for producing a high power, coherent optical laser beam.